Control of the steroidogenic metabolic pathway is regulated partly by P450 cytochrome hydroxylases, and the expression of many of these enzymes is controlled by the orphan nuclear receptor, steroidogenic factor-1 (SF-1).
Steroidogenesis is controlled by the expression of P450 cytochrome hydroxylases that are regulated by the nuclear transcription factor SF-1 (10).
In studies with fetal rat testis, maternal treatment with OP reduced the expression of cytochrome P450 17[alpha]-hydroxylase/C17-20 lyase, an enzyme regulated by SF-1 (15).
Using bullfrog tadpoles, we found a sexually dimorphic pattern of SF-1 protein expression that emerges at the time of gonadal sexual differentiation (16).
The contralateral gonad was harvested, weighed, and snap-frozen in liquid nitrogen for protein extraction and SF-1 protein quantification.
We dropped these animals from the overall analysis for both the Western blot SF-1 determination and sex ratios.
Supernatants were removed and brought up to 500 [micro]L with the tissue lysis buffer and incubated rocking overnight at 4[degrees]C with 5 [micro]g rabbit anti-mouse SF-1 (Upstate Biotech, Lake Placid, NY) per 0.5-1.0 mg sample total protein.
Analysis and quantification of SF-1. To quantitate SF-1 protein expression in the developing frog gonads, we first determined the minimum amount of protein necessary to detect SF-1 in the smallest gonadal sample (16).
Before testing for any significant differences in SF-1 expression among treatments by stage, we tested for homogeneity of variance with an [F.sub.max] test with p = 0.01.
Changes in SF-1 expression as a result of OP treatment in differentiating gonads of bullfrog tadpoles.
The purpose of this study was to determine the effects of the endocrine disrupter OP on gonadal differentiation in bullfrogs and to determine whether there was any detectable disruption in the gonadal expression of SF-1 during this period of development.
However, there are no reports of estradiol or other steroid treatment accelerating bullfrog gonadal differentiation as we found here, and we do not yet know if the change in SF-1 expression we found plays a role in this acceleration.